The objective of this study is to better understand patients' and breast surgeons' perspectives regarding contralateral prophylactic mastectomy (CPM). An estimated 232,340 women will be diagnosed with breast cancer in the United States in 2013. Following diagnosis, women will undergo one of three surgical procedures: 1) breast conserving surgery (BCS), i.e., lumpectomy (removal of the tumor), 2) mastectomy (removal of the breast), or 3) mastectomy plus CPM (removal of the cancerous breast and removal of the other breast). Since 1998, CPM rates have more than doubled among stage I, II or III breast cancer patients and increased by nearly 150 percent among women diagnosed with ductal carcinoma in situ (DCIS, stage 0 cancer). The increase in rates of CPM is a surprising shift toward more aggressive management of breast cancer and represents a widening gap between recommended care and selected care. The National Comprehensive Cancer Network (NCCN) Clinical Practice Guidelines in Oncology for Breast Cancer and the Society of Surgical Oncology discourage CPM except for women considered to be high risk. However, rates of CPM are increasing among women who are not high-risk and who will likely not obtain a survival benefit from the procedure but will face increased risk of surgical complications. Given the risk and expense associated with this major surgical procedure, understanding how and why women make surgical decisions is important. Our study will be among the first to prospectively examine the breast cancer surgical decision making process. Given the lack of studies examining CPM decision making, we will use qualitative and quantitative methods to grow our understanding of this surgical trend. Our application has two aims. Aim 1 will identify and examine the pre-surgical determinants of surgical decisions among DCIS and Stage I-III breast cancer patients. Aim 1 will be accomplished by collecting qualitative and quantitative data via semi-structured interviews with 60 breast cancer patients in the period between surgical consult and surgery. The interview protocol is informed by determinants as identified in the Ottawa Decision Framework. Aim 2 is to examine breast surgeons' views of CPM and their approaches to counseling patients about CPM. Aim 2 will be accomplished by conducting semi-structured interviews with 20 surgical oncologists. The long-term goal of this research is to inform the design of interventions aimed at both physicians and patients to support informed and effective decision making for women with breast cancer.